Friday, December 28, 2012

Who we are, part 1 (Mum)

At last I am able to dilate upon my remote
ancestry, thanks to the National Geographic Society’s Geno 2.0 project, which I
described earlier. The results of their analysis of my mitochondrial DNA and my Y-chromosome arrived when I was in London a
few weeks ago, and I have been gradually absorbing the implications
ever since, most of which are simply awe-inspiring. On the
whole I am thankful that my mother never lived to be vexed by the idea
that it is thanks to her, and her distant relations, that my brothers and I are 2.7% Neanderthal, although
my beloved Lyolik says with firmness that he reckons that this
figure is far too low. Whichever way you look at it, however, there can be no doubt that approximately 60,000 years ago one or quite possibly more of my mother’s female ancestors turned the head of Hairy Slobodan of the Caucasus, some no doubt fetching
Neanderthal, and that this was far more than a brief dalliance; evidently it involved a sustained period of gleefully horizontal folk-dancing
in the flickering light of a fire, perhaps in a cave or escarpment, or in the lea of some convenient, mossy bank (for privacy). Intriguing.

Let us go back to the beginning, however. The common direct maternal ancestor to all people
living today was born in East Africa around 180,000 years ago. Obviously
she was not the only female hominid alive at that remote time, but hers is the
only line of posterity that has survived into current generations. This woman
represents the deepest root of the human family tree. She gave rise to two
descendant lineages known as L0 and L1’2’3’4’5’6, each of which is characterized
by a different set of genetic mutations carried by their respective members.
Current genetic data indicate that indigenous people belonging to these groups
are found exclusively in Africa. This means that, because all humans have in a
common this female ancestor, and because
Africans are the oldest groups on the planet, we know our species—each and
every one of us, the entire human family—originated there. The more historically-minded might choose to
think of this as a distant but satisfactory premonition of gins-and-tonic on the verandahs of
suburban Nairobi or the polo fields of Happy Valley, but in truth we are looking at hairy hominids busying themselves over
tens of thousands of years with the task of basic survival, and the quest
for controllable flame—fire! the earliest glimmer of the pre-dawn of human
civilization—at around the same vital moment as the earliest discovery, or evolution, or invention of language itself, those guttural love cries with which in due course Mum’s people evidently beguiled certain Neanderthals of the Caucasus.

L3

Eventually, by a process of gradual genetic
mutation, L1’2’3’4’5’6 gave rise to L3 in East Africa.
While L3 individuals are found all over Africa, L3 is important because of its movements north. Our L3 maternal ancestors were the first party of Homo sapiens to leave Africa, and therefore represent the deepest
branches of the tree found outside that continent. Thenceforth, members of this
group went in different directions. Many stayed on in Africa, dispersing
to the west and south. Some L3 lineages are predominant in many
Bantu-speaking groups who originated in west-central Africa, later scattering
throughout the continent and spreading this L3 lineage from Mali to South
Africa. Today, L3 is also found in many African-Americans.
Other L3 individuals, however, our ancestors, kept moving northward,
eventually leaving the African continent completely. These people gave rise to
two important haplogroups that went on to populate the rest of the world.

It is likely that a fluctuation in climate may
have prompted our ancestors’ departure from Africa. The African
Ice Age was characterized by drought rather than by cold. Around 60 to 50,000
years ago the ice sheets of northern Europe began to melt, introducing a period
of warmer temperatures and moister climate in Africa. Parts of the inhospitable
Sahara briefly became habitable. As the drought-ridden desert changed to
savanna, the animals our ancestors hunted expanded their range and began moving
through the newly emerging green corridor of grasslands. Our nomadic ancestors
followed the good weather and plentiful game northward across this Saharan avenue, although the exact route they followed remains to be determined.
Whatever the cause of the exodus, it is also clear that when it occurred (a)
there were barely 2,000 individuals of the species Homo sapiens left alive, so
we very nearly became extinct before the long human migrations even began. We survived only by the skin of our teeth; our civilization might never have developed at all.
(b) Those 2,000 shivering, frightened, increasingly desperate specimens were
evidently huddled in and around an area of Ethiopia known as the Asaf
Depression. And that was the point of departure for many tiny groups of the
survivors, of whom a handful actually stayed put.

N

Our next crucial maternal ancestor is the woman
whose descendants formed haplogroup N. Haplogroup N comprises one of two groups
that were created by the descendants of L3. One of these two groups of
individuals moved north rather than east and left the African continent across
the Sinai Peninsula, in what is now Egypt. Also faced with the harsh desert
conditions of the Sahara, these people apparently followed the Nile basin, which yielded a reliable supply of food and water in spite of the surrounding desert
and its frequent sandstorms. Descendants of these migrants eventually formed
haplogroup N. Early members of this group lived in the eastern Mediterranean
region and western Asia, where they apparently co-existed for a time with other
hominids such as Neanderthals. Excavations in the Kebara Cave (Mount
Carmel) in Israel have unearthed Neanderthal skeletons as recent as 60,000 years old,
indicating that there was both ample geographical and chronological overlap between us and them. This accounts for the presence of Neanderthal DNA in those of us who live
outside Africa—between 1% and 4% of the whole of our DNA is Neanderthal.

Be that as it may, after several thousand years in the Near East,
members of our group began moving into unexplored neighboring territories, following
large herds of migrating game across vast plains. These groups broke into
several directions and made their way into territories surrounding the Near
East.Today, haplogroup N individuals who headed west
are prevalent in Turkey and the eastern Mediterranean. They are found farther
east in parts of Central Asia and the Indus Valley of Pakistan and India. And
members of our haplogroup who headed north out of the Levant across the
Caucasus Mountains have remained in southeastern Europe and the Balkans.
Importantly, descendants of these people eventually went on to populate the
rest of Europe, and today comprise the most frequent mitochondrial lineages
found there.

R

After several thousand years in the Near East,
individuals belonging to a new group called haplogroup R began to move out and
explore the surrounding areas. Some moved south, migrating back into northern
Africa. Others went west across Anatolia (roughly corresponding with modern Turkey) and north across
the Caucasus Mountains of Georgia and southern Russia. Still others headed east
into the Middle East, and on to Central Asia. All of these individuals had one
thing in common: they shared a female ancestor from the N clan, a recent
descendant of the migration out of Africa.

The story of haplogroup R is complicated,
however, because these individuals can be found almost everywhere, and because
their origin is quite ancient. In fact, the ancestor of haplogroup R lived
relatively soon after humans moved out of Africa during the second wave, and
her descendants undertook many of the same migrations as her own group, N.Because the two groups lived side by side for
thousands of years, it is likely that the migrations radiating out from the
Near East comprised individuals from both of these groups. They simply moved
together, bringing their N and R lineages to the same places around the same
times. The tapestry of genetic lines became quickly entangled, and geneticists
are currently working to unravel the different stories of haplogroups N and R,
since they are found in many of the same far-flung regions.

U

Descending from the R group, a woman gave rise to
people who now constitute haplogroup U. Because of the great genetic diversity
found in haplogroup U, it is likely that this woman lived around 47,000 years
ago. Let us call her Granny Ugh!Her descendants gave rise to several different
subgroups, some of which exhibit very specific geographic homelands. The very
old age of these subgroups has led to a wide distribution; today they harbor numerous particular European, northern African, and Indian components, and are to be found in
Arabia, the northern Caucasus Mountains, and throughout the Middle and Near East.

One interesting subgroup is U6, which branched
off from haplogroup R while still in the Middle East, moved southward, and
today is found in parts of northern Africa. Today, U6 individuals are found in
around 10% of people living in North Africa. However, other members of the larger haplogroup U descend
from a group that moved northward out of the Near East. These women crossed the
rugged Caucasus Mountains in southern Russia, and moved on to the steppes of
the Black Sea. These individuals represent movements from the Black Sea steppes
west into regions that comprise the present-day Baltic States and western
Eurasia. This grassland then served as the springboard for subsequent movements
north and west.

Today, this line is part of populations in
Europe, West Asia (including Arabia), North Africa, India, and the North
Caucasus Mountains. In Europe, this lineage averages 7% of the
population. In Scandinavian countries (Norway, Sweden, the Netherlands, etc.)
it is between 9% and 16% of the population. In England, it is about 12% of the population. Toward the Mediterranean, this line is between 10% and 12% of the population in Croatia and Greece.

U5

The most recent common ancestor for all of us U5
individuals broke off from the rest of the group and headed north into
Scandinavia. Even though U5 is descended from an ancestor in haplogroup U, it
is also exceedingly ancient, and thought to be around 30,000 years old.

U5 is quite restricted in its variation to
Scandinavia, and particularly to Finland. This is probably the result of the
significant geographical, linguistic, and cultural isolation of the Finnish
populations, which restricted geographic distribution of this
subgroup and kept it genetically isolated. The Saami, reindeer hunters
who follow the herds from Siberia to Scandinavia each season, have the U5
lineage at a very high frequency of around 50%, indicating that it may have
been introduced during their movements into these northern territories.

The U5 lineage is found outside Scandinavia,
though at much lower frequencies and at lower genetic diversity. Interestingly,
the U5 lineage found in the Saami has also been found in some North African
Berber populations in Morocco, Senegal, and Algeria. Finding similar genetic
lineages in populations living thousands of miles apart is certainly
unexpected, and is likely the result of re-expansions that occurred after the
last glacial maximum around 15,000 years ago. Humans who had been confined to
narrow patches in southern Europe began to move outward again, re-colonizing
ancient territories and bringing new genetic lineages with them.

In addition to being present in some parts of
North Africa, U5 individuals also live sporadically in the Near East at 2%—about one-fifth as frequent as in parts of Europe—and are completely
absent from Arabia. Their distribution in the Near East is largely confined to
surrounding populations, such as Turks, Kurds, Armenians, and Egyptians.
Because these individuals contain lineages that first evolved in Europe, their
presence in the Near East is the result of a back-migration of people who left
northern Europe and headed south, as though retracing the migratory paths of
their own ancestors.

U5B

Today, this line is present most often in Finland
(15%) and Latvia (12%). It is between 6% and 9% of maternal
lineages in Luxembourg, Northern Ireland, Spain, and Slovenia.
It is widespread in western Eurasia, particularly to
the north. This spread began with the expansion of haplogroup U5B-bearing
populations out of West Asia during the Upper Paleolithic, prior to 12,000
years ago, and like other branches of U it reached Europe during the
Paleolithic. Despite later waves of migrants from other lineages, it remains
common there.

Insomma, we can now conclude (not very
surprisingly) that Mum’s distant relations down to approximately 10,000 years
ago were only 45% Northern European, and that that component of our ancestry is
found at the highest frequency in Britain, Denmark, Finland, Russia and Germany (oh!).
While not limited to these groups, it is found at significantly lower frequencies throughout
the rest of Europe. This component is probably the signal of the earliest
hunter-gatherer inhabitants of Europe, who were the last to make the transition
to agriculture as it moved in from the Middle East during the Neolithic period
around 8,000 years ago—Hairy Grandmother Margaret on her wee Shetland pony, as Hamish rightly predicted, galloping
headlong across the land bridge into the vastnesses of the Scottish highlands at almost the very
earliest time that this was possible. Is it any wonder therefore that on my
first visit to Edinburgh some years ago I had the strongest feeling that I had
been there before?

On the other hand we of the line of U5B are also 37%
Mediterranean, a component to be found at the highest
frequencies in southern Europe and the Levant—people from Sardinia, Italy,
Greece, Lebanon, Egypt and Tunisia. While not limited to these groups, it is
found at lower frequencies throughout the rest of Europe, the Middle East,
Central and South Asia. This component is also probably a sign of the Neolithic
population expansion from the Middle East, beginning around 8,000 years ago,
likely from the western part of the Fertile Crescent.

We are also 17% Southwest Asian.This component of our ancestry is found at highest frequencies in
India and neighboring populations, including Tajikistan and Iran—and it is
probably just as well that Mum never lived to learn this, although I am quite
sure that she would have looked askance with her customary pursed-lip
skepticism. Nevertheless this component is an undeniable fact of our mitochondrial DNA, and it is also found at significantly lower frequencies in
Europe and North Africa. As with our Mediterranean component, it was most probably
spread during the Neolithic expansion, perhaps from the eastern part of the
Fertile Crescent. Individuals with heavy European influence in their ancestry
will show traces of this because all Europeans have mixed with people from
Southwest Asia over tens of thousands of years, something that was not lost on
Grandfather Borthwick and his slightly crude allegation that there was, at least in the
Borthwick line, a “touch of the tar-brush.” Putting it in a slightly more positive light, Mum carried a modicum of the culture of primitive near-eastern philosophy, mathematics, jurisprudence, and the root of writing itself, and no doubt this expressed itself in the skills she duly brought to The Times cryptic crossword puzzle, and to the bridge table.

For all of this we must be grateful, and now to Dad and the Y-chromosome.

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About Me

Angus Trumble will begin work as Director of the National Portrait Gallery of Australia on February 10, 2014. He has been Senior Curator of Paintings and Sculpture at the Yale Center for British Art in New Haven, Connecticut, since May 2003.
Angus is the author of a number of books, including A Brief History of the Smile and The Finger: A Handbook, which has lately been published in New York by Farrar, Straus, and Giroux, in London by Yale University Press, and by Melbourne University Publishing. He is an occasional contributor to the Burlington Magazine, Apollo, and a more regular one to The Times Literary Supplement, the Australian Book Review, and Esopus Magazine.